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ARRL Propagation Bulletin ARLP033 (2001)

ARLP033 Propagation de K7VVV

QST de W1AW  
Propagation Forecast Bulletin 33  ARLP033
From Tad Cook, K7VVV
Seattle, WA  August 10, 2001
To all radio amateurs 

ARLP033 Propagation de K7VVV

Sunspot numbers and solar flux rose quite a bit this week. Sunspot
numbers peaked on Sunday at 214, the highest since June 25. Average
sunspot numbers rose over 83 points and average solar flux was up
over 32 since the previous week. Sunday and Monday of this week were
active geomagnetically. This increases absorption of HF radio
signals, particularly in the higher latitudes. The planetary A index
on both days was high at 23 and 21, and the College A index reported
from Fairbanks, Alaska was 37 and 29. 37 indicates a severe storm,
and there were three reporting periods on August 5 with K indices at
6, which is very high. For more information on the relationship
between K and A indices, check

Conditions have been quiet for the past few days, but this Sunday,
the second day of the Worked All Europe DX CW Contest, geomagnetic
activity should rise again. The projected planetary A index for
Friday through Monday is 10, 10, 25 and 20. Predicted solar flux for
those same days is 155, 150, 150 and 145. Conditions should be good
for the first day of the contest at least. The reason for the
predicted rise in geomagnetic instability on Sunday is a solar wind
blast from a coronal hole which should affect earth that day. But on
Thursday a coronal mass ejection appeared, which could bump the A
index even higher over the weekend.

Earlier this week was the halfway point from the summer solstice to
the fall equinox. Fall is a great time for HF radio propagation,
especially on the higher HF bands, and we should gradually see a
drift from summer to fall conditions.

Both N1AW and KF2YP wrote to inquire about the source of the
holographic images of the sun's backside, referred to in last week's
Propagation Forecast Bulletin ARLP032. These are shown at and an explanation of this technique for
peering through the sun is at

Since there is a lot of interest among contesters this weekend in
propagation to Europe, we will include toward the end of this
bulletin a few path projections for the Worked All Europe DX CW
Contest. But first, there have been numerous requests to run the
explanation again for some of the numbers used in this bulletin. It
was last run a little over a month ago, but here it is again.

Amateur Radio operators who use HF generally like increased sunspots
because they correlate with better worldwide radio propagation.
When there are more sunspots, the sun puts out radiation which
charges particles in the earth's ionosphere. Radio waves bounce off
of (refract from) these charged particles, and the denser these
clouds of ions, the better the HF propagation.

When the ionosphere is denser, higher frequencies will refract off
the ionosphere rather than passing through to outer space. This is
why every 11 years or so when this activity is higher, 10 meters
gets exciting. 10 meters is at a high enough frequency, right near
the top of the HF spectrum, that radio waves propagate very
efficiently when the sunspot count is high. Because of the shorter
wavelength, smaller antennas are very efficient on this band, so
mobile stations running low power on 10 meters can communicate world
wide on a daily basis when the sunspot cycle is at its peak. There
are also seasonal variations, and 10 meters tends to be best near
the spring or fall equinox.

The sunspot numbers used in this bulletin are calculated by counting
the spots on the visible solar surface and also measuring their

Solar flux is another value reported in this bulletin, and it is
measured at an observatory in Penticton, British Columbia using an
antenna pointed toward the sun hooked to a receiver tuned to 2.8
GHz, which is at a wavelength of 10.7 cm. Energy detected seems to
correlate somewhat with sunspots and with the density of the

Other solar activity of concern to HF operators are solar flares and
coronal holes, which emit protons. Since the charged ions in the
ionosphere are negative, a blast of protons from the sun can
neutralize the charge and make the ionosphere less refractive.
These waves of protons can be so intense that they may trigger an
event called a geomagnetic storm. In addition, energy from a solar
flare may energize the D-layer of the ionosphere, which absorbs
radio waves.

The Planetary A index relates to geomagnetic stability.
Magnetometers around the world are used to generate a number called
the Planetary K index.

A one-point change in the K index is quite significant. K index
readings below 3 generally mean good stable conditions, and above 3
can mean high absorption of radio waves. Each point change reflects
a big change in conditions.

Every 24 hours the K index is summarized in a number called the A
index. A one-point change in A value is not very significant. A full
day with the K index at 3 will produce an A index of 15, K of 4
means A of 27, K of 5 means A of 48, and K of 6 means A of 80.

The geomagnetic number reported here is the Planetary A index, which
is a worldwide average based on the K index readings from a number
of magnetometers. The numbers reported on WWV are the Boulder K and
A index, measured in Colorado. Generally the higher the latitude of
the measuring station, the higher the K and A indices reported.
This is because the effects of geomagnetic instability tend to
concentrate toward the polar regions of the globe. You can hear the
Boulder K index updated every three hours on WWV, or by calling

Here are the path projections to Europe for this weekend. K9GY asked
for them, and first are his projections for the best times to work
Europe from the East Coast. 80 meters, 0200-0300z and 0400-0500z, 40
meters, 2300-0900z, 20 meters always open, 15 meters 0900-2300z, and
10 meters 1000-2000z.

Here are my projections.

From Philadelphia, 80 meters 2330-0530z (best 0230-0300z), 40 meters
2200-0630z (best 0030-0330), 20 meters 1830-0600z (best 0000-0230),
15 meters possibly 1230-0030z (best 1930-2000), 10 meters possibly
1330-1400 and 1500-1800z.

From Atlanta, 80 meters 0030-0530z, 40 meters 2300-0630z (best
0130-0400), 20 meters 2000-0630 and 0930-1100z, 15 meters
1700-0030z, 10 meters possibly 1300-2230z.

From Dallas, 80 meters 0100-0430z, 40 meters 0030-0600z, 20 meters
2200-0230 and 0430-0730z, 15 meters possibly 1430-2330z, 10 meters
possibly 1500-1530 and 1630-1930z.

From Cleveland, 80 meters 0030-0500z, 40 meters 2300-0630z, 20
meters open most hours, best 0000-0300z, weakest 0730-1030 and
1230-1730z, 15 meters possibly 1330-0030z, 10 meters possibly

From Omaha, 80 meters 0130-0430z, 40 meters 0030-0530z, 20 meters
2030-0200 and 0430-0630z, 15 meters possibly 1200-0030z.

From Salt Lake City, 80 meters 0300-0400z, 40 meters 0200-0530z, 20
meters 2230-0230 and 0430-0830z, 15 meters possibly 1300-0100, best
bet 1800-2300z.

From California, 80 meters 0330-0400z, 40 meters 0230-0500z, 20
meters 2300-0830z, 15 meters possibly 1300-0100 and 0500-0730, best
bet 1600-2300z, 10 meters possibly 1800-2100z.

From Seattle, 40 meters 0230-0500z, 20 meters 2200-0200 and
0400-0830z, 15 meters possibly 1330-0330z.

From Alaska, 20 meters 0330-1200 and 1330-0100z, 15 meters 0730-0900
and 1800-2300z.

From Hawaii, 20 meters 0400-0730z, 15 meters 1630-2000 and possibly
0730-1100z, 10 meters possibly 0900-0930, 1630-1700 and 1800-2030z.

Sunspot numbers for August 2 through 8 were 113, 140, 182, 214, 182,
177 and 191 with a mean of 171.3. 10.7 cm flux was 120.8, 131.6,
148.4, 156, 163.7, 166.3 and 166.9, with a mean of 150.5, and
estimated planetary A indices were 8, 14, 9, 23, 21, 13 and 9 with a
mean of 13.9.


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